Imported plants, which are now valued at more than $500 billion annually, may be a boon for the U.S. economy, but are having a devastating effect on the environment.

A study conducted by researchers at University of California, Santa Barbara’s National Center for Ecological Analysis and Synthesis finds that almost 70 percent of the most damaging non-native forest insects and diseases currently afflicting U.S. forests arrived via imported live plants.

Published in the journal Frontiers in Ecology and the Environment, the study shows that in the last 43 years, the quantity of plant imports to the U.S. has risen by more than 500 percent, peaking at 3.15 billion plants in 2007. Nearly half of the imported live plants entering the U.S. are destined for either California or Florida.